@rnd_normal(μ:float, σ:float)
returns a random generator that produces floating-point values according to a normal distribution P:
P(x | μ, σ) = 1/(σ \sqrt{2 π}) e^{- (x - μ)^2/(2 σ^2)}
See @rnd_bernoulli for a description of random generators.
See also Random Generators @rand, @rand_int, @random, @rnd_bernoulli, @rnd_binomial, @rnd_exponential, @rnd_gamma, @rnd_geometric, @rnd_normal, @rnd_uniform_float, @rnd_uniform_int